Multiplexing and especially statistical multiplexing as well as re-scheduling of media packets offer a better utilization of bandwidth limited communication channels.
Encryption of media streams is used in conditional access systems. A media stream can be scrambled with a secret control word. The control word can be encrypted before it is transmitted to a receiver as an entitlement control message (ECM). The receiver will decrypt the control word only when authorized to do so—when it receives an entitlement management message (EMM). The EMMs can be allocated per user.
Combining encryption techniques with statistical multiplexing and/or re-scheduling poses various problems.
Performing multiplexing before encryption is a resource-consuming solution when the same media stream should be sent over multiple channels—so it has to be encrypted several times.
Another approach limits the bit rate of the media stream to provide constant bit rate media streams of a reduced bit rate in order to guarantee that the media stream, after the encryption, will not exceed an allowable threshold. This approach can unnecessarily limit the bit rate of the media stream, resulting in lower quality and even in an inefficient utilization of channel bandwidth.
There is a growing need to provide efficient methods, systems and computer program products for manipulating media streams.